Hot press/cold press operations are well known in the tile making art. See, for example, Loetscher U.S. Pat. No. 1,825,877 wherein a coating layer is embossed and fused to the remainder of the tile structure in a press having platens to which steam is applied. Before the pressure is relieved, the steam shut off and water circulated through the platens to reduce the temperature of the tile product.
Also note British Patent Specification No. 1,366,494 of Severus et al. which is directed to a method of making multi-layer laminates using two presses, one heated to laminate the product and the second cooled to reduce the temperature of the laminated product while under pressure of the second press. At lines 28 to 34 on page 1, Severus et al. discuss expelling the air between the individual layers of the material by repeated closing and opening of the press.
Becker et al. U.S. Pat. No. 4,747,901 also discloses a hot press/cold press laminating and embossing process for the production of floor and wall tile. They also disclose the use of porous layers to allow the passage of air through the thickness of the tile material.
The use of high frequency electrical energy and pressure to form a floor or wall tile is disclosed in Creighton et al. U.S. Pat. No. 4,604,312. They too use a porous, thermoplastic base material and a perforated film.
As identified by the above patent references, the problem of air entrapment between the upper exposed surface of the tile and the embossing plate has been appreciated by those skilled in the art. The entrapped air prevents 100% intimate contact of the tile wear layer with the embossing plate and causes unintended areas of high gloss on the exposed surface of the finished tile product. These areas of high gloss are typically 1/4 of an inch to 11/2 inches in dimension.
This problem has been significantly reduced by the use of porous starting materials. However, the prior art has been unable to produce gloss defect-free tile having a substantially non-porous base layer. Particularly, if the tile has a mortar-line surround design. Many tile designs include a mortar-line surround pattern which is an embossed depression surrounding the periphery of the tile and resembles a mortar or grout line between two ceramic tile. The mortar-line surround helps to hide the tile seams.
It is an object of the invention to provide a method of producing gloss defect-free tile having a substantially non-porous base, even if the tile has a mortar-line surround pattern.
A further object is to provide a process to produce a tile having intricate and detailed embossed patterns which are in precise registration with a printed image and includes multiple levels of gloss and a mortar-line surround pattern. Such a tile product can only be formed if there is 100% intimate contact between the wear layer and embossing mold. As discussed previously, entrapped air forms unintended areas of high gloss which destroy the intended embossing pattern. Entrapped air is a particularly pronounced problem if the tile has a mechanically embossed mortar-line surround pattern.
Another object is to provide a process which enables the use of inexpensive embossing plates or molds which will be able to produce the intricate and detailed embossing patterns.
Yet another object is to provide a process which produces a curl free tile having different binder levels in the base and wear layer.
Other objects and advantages of the invention will become apparent upon reading the following detail description.